Resonant Transformer

ABSTRACT

Exemplary embodiments of the present disclosure are directed to resonant transformers (or reactors) and coil arrangements associated with resonant transformers. The coil arrangements can include a grounding coil configured to generate a net-zero induced voltage between a first end of the grounding coil and a second end of the grounding coil layer, and one or more step-up coil layers formed by one or more layers of pressure tape, insulating materials, and wire wrapped to form coils about a portions of a split magnetic core. The split magnetic core can include a first core segment and a second core segment, where one of the core segments is disposed within a main housing and one of the core segments is disposed external to the main housing. A gap between the first and second core segments can be manipulated to control an inductance of the resonant transformer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/505,872, filed on Oct. 3, 2014, the disclosure of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

Exemplary embodiments of the present disclosure are directed totransformers, and more particularly, to resonant transformers and coilarrangements associated therewith.

BACKGROUND

Installed electrical power equipment is often subjected to diagnostictests, such as partial discharge tests, requiring high alternatingvoltage at power frequency. Regular power frequency voltage sourcesconventionally used in factories for high voltage tests typicallyinclude relatively heavy and bulky transformers that are not practicalfor use in the field where installed equipment needs to be tested.Fortunately, when the electrical equipment to be tested can beconsidered as an electrical capacitor, as is the case for an electricalpower cable, it is possible to generate a desired test voltage using aresonant transformer (also referred to herein as “reactor”), which isoften significantly smaller and lighter than a regular transformer ofthe same rating, and can be transportable to sites outside the factory.If L is the inductance of the resonant transformer, C is the capacitanceof the cable to be tested, and f is the frequency of a voltage sourceinput to the resonant transformer, resonance is said to be achieved when2πfL=1/(2πfC). Under resonance conditions, the voltage across the testcable becomes a large multiple, Q, of that of the alternating voltagesource, where Q is referred to as the quality of the circuit. Thus,starting with a modest voltage magnitude (e.g., ˜1 kV), it is possibleto generate a high voltage (e.g., ˜25 kV to ˜75 kV).

The capacitance of a given type of cable to be tested variesproportionally with the length of the cable. That is, as the length of agiven cable type increases, the capacitance of the cable increasesproportionally. In order to achieve resonance for different lengthcables, either inductance L or frequency f or both have to be adjustedaccordingly. In some conventional systems, the resonant transformer canbe configured to generate a variable inductance L to achieve a desiredinductance value for a given capacitance to be tested.

To achieve a variable inductance resonant transformer, a high voltagewinding, sometimes split over two coils, is built around one or two legsof a magnetic core that is split to form two U-shaped magnetic pathsfacing each other across open air gaps. While one of these U-shapedcores is stationary, the other is connected to mechanical actuatorswhich allow the gap to open or close. The entire assembly, including themechanical actuators, are generally housed in a relatively large metaltank, normally filled with insulating oil to provide dielectricstability to the coil of the resonant transformer (e.g., to inhibitundesirable discharges in the coil). The forces of electromagneticorigin on the faces of the core across air gaps tend to dictatemechanical and structural designs which result in heavy core assemblies.When testing objects of small capacitance, such as short cables, withcommercially available variable inductance transformers, resonance isoften not achievable and complex schemes have to be developed toaccommodate small capacitance. For example, in one conventional scheme,the resonant transformer can be connected in parallel with the cable,while allowing the resonant transformer to function as anauto-transformer. Furthermore, with cables of large capacitance, the airgap is often forced to assume large values (e.g., approximately 15 cm ormore). As a result, the tank housing of the resonant transformertypically must be much larger (and heavier) than desired to accommodatemovement of the split magnetic core. Another major contribution to theweight of such transformers is the insulating oil used in the tank.

SUMMARY

To overcome the problems associated with conventional resonanttransformers (or reactors), exemplary embodiments of the presentdisclosure advantageously provide for resonant transformers that have asubstantial weight and volume reduction as compared to conventionalresonant transformers, resulting in smaller and more fuel-efficient testvehicles for transporting the resonant transformers to perform fieldtesting of cables, while achieving a wide range of inductances that canallow users to avoid complicated schemes when testing short cableshaving relatively low capacitance. Exemplary embodiments can be safelyand effectively operated without using heavy and environmentallyunfriendly insulating oil to facilitate dielectric stability in the coilof the resonant transformer.

Exemplary embodiments of the present disclosure provide for resonanttransformers (or reactors) including a magnetic core having a first coresegment and a second core segment that can form a gap that is devoid ofmagnetic material, where a size of the gap can control an inductance ofthe resonant transformer. Exemplary coil arrangements of the resonanttransformers are described herein to provide for stable operation of theresonant transformers (e.g., at tens or hundreds of kilovolts) whenexposed to the atmosphere by using a coil arrangement having a groundingcoil layer that is wound to generate a net zero induced voltage betweenthe ends of the grounding coil and sequentially stepped or gradedstep-up coil layers including pressure tape (such as mylar tape) andinsulating material (such as ethylene-propylene rubber (EPR) tape). Thecoil arrangements can include one or more taps to allow the resonanttransformer to output intermediate voltages in addition to the voltagesthat can be output by the end of the wire that forms the step-up coils.

In accordance with some embodiments of the present disclosure, at leasta portion of the resonant transformer including the coils can bedisposed in a sealed main housing that is maintained at atmosphericpressure or a relatively low pressure nitrogen gas, while portions ofthe resonant transformer, such as a portion of the magnetic core can bepositioned external to the housing. By positioning one of the coresegments externally to the housing, exemplary embodiments of the presentdisclosure can further reduce the size and weight of embodiments of theresonant transformers described herein as compared to conventionresonant transformers.

When embodiments of the coil arrangements described herein are utilizedin the resonant transformer, the housing can be filled with air (at alow humidity) or an inert gas, such as nitrogen, as opposed to aninsulating oil, due to the reduced likelihood of undesirable electricaldischarges from the coil arrangements. By using a housing that is filledwith air or an inert gas at a relatively low pressure, the weight ofexemplary embodiments of the resonant transformers described herein canbe substantially reduced as compared to conventional resonanttransformers housed in a tank filled with an insulating oil. Forexample, exemplary embodiments of the present disclosure can weigh atleast thirty-five (35) percent less than conventional resonanttransformers housed in a tank filled with an insulating oil.

For embodiments of the resonant transformers that utilize multiple coils(e.g., two coils), the coils can be used independently of each other,electrically connected in parallel, or electrically connected in serieswith each other. To form a resonant circuit, the resonant transformer iselectrically coupled, in series, with a capacitive load. That is,whether an output of the resonant transformer is generated by a singlecoil, both coils operating in parallel with each other, or both coilsoperating in series with each other, the output of the resonanttransformer is electrically coupled in series to a capacitive load. Asone example, when the two coils are configured in parallel with oneanother, both of the coils can be operatively coupled to a capacitiveload such that the parallel configuration of coils are electricallyconnected in series with the capacitive load. As another example, whentwo coils are connected in series one of the coils can receive an inputvoltage and can output an intermediate voltage to the input of thesecond coil, and an output of the second coil can be operatively coupledto a capacitive load such that the coils and the capacitive load are inseries with each other. The use of a single coil, two coils in parallel,and/or two coils in series can facilitate a wide range of inductances ofthe resonant transformers described herein, and a wide range of outputvoltages and output currents from the resonant transformers.

In accordance with embodiments of the present disclosure, a transformeris disclosed that includes a main housing, a split magnetic core, and acoil. The split magnetic core has a first core segment and a second coresegment. The first core segment is disposed within the main housing andthe second core segment can be disposed external to the main housing. Atleast one coil is wrapped around the first core segment. A gap betweenthe first and second core segments is manipulated to adjust aninductance of the split magnetic core. The housing can be filled with adry air or an inert gas (e.g., nitrogen) that is maintained under modestpressure and the second core segment can be exposed to atmosphericpressure. The first core segment can have at least one of a U-shapedconfiguration or a C-shaped configuration, and the second core segmentcan have an I-shaped configuration.

In accordance with embodiments of the present disclosure, the secondcore segment can be moveable with respect to the first core segment. Forexample, exemplary embodiments can include an actuator that is operativeto move the second core segment with respect to the first. Anon-magnetic member, such as a solid insulating insert or an inflatablemember, can be configured to be disposed between the second core segmentand the first core segment to limit a movement of the second coresegment towards the first core segment during an operation of thetransformer as well as to limit mechanical vibrations of the second coresegment. A resilient member can be configured to urge the second coresegment towards the first core segment such that the second core segmentcan be held in compressionwith the non-magnetic member.

In accordance with embodiments of the present disclosure, a distancebetween the second core segment can be fixed with respect to the firstcore segment to define a maximum gap size. An actuator can beoperatively coupled to a magnetic insert member, and the actuator can beconfigured to move the magnetic insert member with respect to the firstand second core segments to position the magnetic insert member in thegap between the first and second core segments to adjust the size of thegap and the inductance of the transformer.

In accordance with embodiments of the present disclosure, the first coresegment can be permanently connected to (or integrally formed with) thesecond core segment, and both core segments can be located within themain housing. A slice of magnetic material can be removed from thesecond core segment, forming a notch in the second core segment that isdevoid of magnetic material to define a maximum size of the gap. Thehousing can conform to the notch to follow a contour of the notch toform a recess in the housing extending into the notch. The size of thegap can be modified by inserting in the notch, from outside of thehousing, an insert formed of a magnetic material of variable thicknessand a non-magnetic material, which may include an inflatable material.The insert can be received in the recess to completely and snugly fillthe recess and the notch to reduce the size of the gap. An actuator canbe configured to move the insert into and out of the recess (and thenotch) to adjust the inductance of the resonant transformer. In someembodiments, the insert can be disposed within the housing and can bemoved into and out of the notch by the actuator.

A coil arrangement about the core can include a grounding coil layer andat least one step-up coil layer. The grounding coil layer can be formedby a ground wire that is wrapped about a core mandrel surrounding aportion of the first core segment in more than one direction. Forexample, the grounding coil can include a first number of turns in afirst direction and the same number of turns in a second directionopposite the first direction. The grounding coil layer can be surroundedby a layer of insulating material. The at least one step-up coil caninclude a course of step-up wire wrapped generally circumferentiallyabout the layer of insulating material, wherein the course of thestep-up wire in the step-up coil layer can be sandwiched betweencoaxially extending layers of insulating pressure tape. A layer ofinsulating material is disposed generally circumferentially over anouter layer of the pressure tape.

Further step-up coil layers can be disposed coaxially and concentricallyover preceding step-up coils, and can include a further course of thestep-up wire, a further layer of pressure tape disposed coaxially andconcentrically over each further course of the step-up wire, a furtherlayer of insulating material disposed coaxially and concentrically overeach further layer of pressure tape, and a still further layer ofpressure tape disposed coaxially and concentrically over each furtherlayer of insulating material.

In accordance with embodiments of the present disclosure, a coilarrangement for a transformer is disclosed. The coil arrangementincludes a grounding coil wound coaxially and concentrically over anon-metallic mandrel that covers the core. The mandrel can have across-section that generally corresponds to a shape of a cross-sectionof the core, but the mandrel can have rounded, smooth corners. Thegrounding coil is wound in alternating directions along a portion of themagnetic core to generate an induced net voltage between a first end ofthe grounding coil and a second end of the grounding coil that issubstantially zero. In some embodiments, the grounding coil can be wounda first number of turns in a first generally circumferential direction(e.g., clockwise) about the magnetic core and wound a second number ofturns in a second generally circumferential direction (e.g.,counterclockwise) about the magnetic core. In some embodiments, thefirst number of turns can be disposed adjacent to the second number ofturns, and the first number of turns equals the second number of turns.In some embodiments, the coil arrangement can include several layers ofinsulating material disposed coaxially and concentrically over thegrounding coil about a portion of a magnetic core of the transformer andcan be sandwiched between layers of pressure tape.

Any combination or permutation of embodiments is envisioned. Otherobjects and features will become apparent from the following detaileddescription considered in conjunction with the accompanying drawings. Itis to be understood, however, that the drawings are designed as anillustration only and not as a definition of the limits of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a resonant transformer having multiplecoils and taps in accordance with exemplary embodiments of the presentdisclosure.

FIG. 1B is a schematic diagram illustrating an exemplary geometry andstructure of the resonant transformer of FIG. 1A in accordance withexemplary embodiments of the present disclosure.

FIG. 2 depicts a cross-section of an exemplary portion of a coilarrangement taken transverse to a central axis of the coil arrangementin accordance with exemplary embodiments of the present disclosure.

FIG. 3 depicts a cross-section of an exemplary portion of a coilarrangement taken along a central axis of the coil arrangement inaccordance with exemplary embodiments of the present disclosure.

FIG. 4 is a schematic diagram of an exemplary winding of wire to form agrounding coil for a coil arrangement in accordance with exemplaryembodiments of the present disclosure.

FIG. 5 is a schematic diagram of an exemplary electrical stress controlarrangement for a coil arrangement in accordance with exemplaryembodiments of the present disclosure.

FIG. 6 depicts an exemplary main housing within which at least a portionof the resonant transformer of FIGS. 1A-B can be disposed in accordancewith exemplary embodiments of the present disclosure.

FIG. 7A depicts a schematic diagram of a resonant transformer inaccordance with exemplary embodiments of the present disclosure.

FIG. 7B depicts a schematic diagram of a resonant transformer having asingle coil in accordance with exemplary embodiments of the presentdisclosure.

FIG. 7C depicts a schematic diagram of a resonant transformer of FIG. 7Awith an inflatable member to stabilize a portion of a split magneticcore in accordance with exemplary embodiments of the present disclosure.

FIGS. 8A and 8B are schematic diagrams of a resonant transformer inaccordance with exemplary embodiments of the present disclosure.

FIG. 8C depicts a schematic diagram of a resonant transformer of FIGS.8A and 8B with inflatable members to stabilize a portion of a splitmagnetic core in accordance with exemplary embodiments of the presentdisclosure.

FIG. 9 is a schematic diagram of a resonant transformer in accordancewith exemplary embodiments of the present disclosure that utilizes aninsert to vary an inductance of the resonant transformer.

FIGS. 10A and 10B are schematic diagrams of a resonant transformer inaccordance with exemplary embodiments of the present disclosure that useinflatable members to adjust an inductance of the resonant transformer.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are related to resonanttransformers (or reactors) including a magnetic core having a first coresegment and a second core segment that can define a gap, where a size ofthe gap can control an inductance of the resonant transformer. The gapcan be manipulated to control the inductance by moving the second coresegment towards or away from the first core segment and/or bymaintaining a distance between the first core segment and the secondcore segment and introducing a magnetic insert member into the gap toreduce the size of the gap.

According to exemplary embodiments, the resonant transformers can have aU/I magnetic core arrangement (i.e. a magnetic core having a U-shapedsegment and an I-shaped segment). One or more coil arrangements can beformed over one or both legs of the U-shaped portion of the magneticcore. Because the magnetic core can have a generally rectangularcross-section with generally sharp edges, a non-metallic, non-magneticcore mandrel that has a cross-sectional shape that generally coincideswith the cross-sectional shape of the magnetic core, but which hasgenerally rounded, smooth edges, can cover the legs of the U-shapedsegment of the magnetic core. The coil arrangements can be wrapped overthe core mandrel. In some embodiments, the I-shaped segment of the corecan be moveable with respect to the U-shaped segment of the core toadjust a gap between the U-shaped segment and the I-shaped segment tovary the inductance of the resonant transformers. While exemplaryembodiments are described as having a U-shaped segment, those skilled inthe art will recognize that other geometries may be used to form themagnetic core. For example, in exemplary embodiments, a C-shaped coremay be used instead of a U-shaped core.

The coil arrangement(s) can provide for stable operation of the resonanttransformers described herein (e.g., at tens or hundreds of kilovolts)without a protective housing and without requiring the use of insulatingoils that are commonly required for the operation of conventionalresonant transformers to prevent undesirable and dangerous electricaldischarges between the step-up or build-up coils and ground. Thus,exemplary embodiments of the present disclosure can be stably operatedwhen exposed to the atmosphere at atmospheric pressure and operating atvoltages upwards of tens or hundreds of kilovolts. As a precaution, inexemplary embodiments of the present disclosure, at least the U-shapedsegment of the magnetic core and the coil arrangements can be disposedin a sealed main housing that is maintained at atmospheric pressure orat a relatively low pressure inert gas, such as nitrogen. By positioningone of the core segments externally to the housing, exemplaryembodiments of the present disclosure can further reduce the size andweight of embodiments of the resonant transformers described herein ascompared to convention resonant transformers. The housing can be filledwith air (at a low humidity) or an inert gas, such as nitrogen. Fillingthe housing with air or an inert gas at a relatively low pressure, asopposed to an insulating oil, allows a weight of exemplary embodimentsof the resonant transformers described herein to be substantiallyreduced as compared to conventional resonant transformers housed in atank filled with an insulating oil. Exemplary embodiments of the presentdisclosure can weigh approximately thirty-five (35) to approximatelysixty-five (65) percent less than conventional resonant transformershoused in a tank filled with an insulating oil. For example, anexemplary embodiment of the resonant transformer including two coils canweigh approximately 1,100 to approximately 1,200 pounds, while aconventional resonant transformer can weigh over 3,000 pounds.

In exemplary embodiments, a structure of the coil arrangements describedherein can include a grounding coil layer and one or more step-up coillayers that are configured to reduce the likelihood of undesirableelectrical discharges as compared to conventional resonant transformers.The coil arrangements can include as many step-up coil layers asnecessary to achieve a total number of turns required to output adesired voltage from the resonant transformer. For example, in anexemplary operation, the resonant transformers can be used to testelectrical cables at various operating voltages, the number of step-upcoils (and total number of turns associated with the step-up coils) canbe specified to meet a voltage rating of the resonant transformer tooperate at the various operating voltages. The grounding coil can bewound over the core mandrel for a specified number of turns inalternating directions to generate a net induced voltage of zero betweena first end of the grounding coil and a second end of the groundingcoil.

The step-up coil layers can be wrapped in successive layers coaxiallyand concentrically over the grounding coil layer, and each successivelywrapped step-up layer can have fewer turns than preceding step-up layers(e.g., two or four fewer turns for each successive step-up layer). Usingthis approach, the step-up coil layers can have a stepped or gradedconfiguration defining a sloping profile along the ends of the coilarrangement. In exemplary embodiments, an insulating material can bedisposed between the grounding coil and the step-up coil layer, andbetween successive step-up coil layers to electrically insulate thegrounding coil and step-up coils from each other, and the step-up coilscan be sandwiched between layers of insulating pressure tape.

For embodiments of the resonant transformers that utilize multiple coils(e.g., two coils), the coils can be electrically connected in parallelor series with each other. As one example, when the two coils areconfigured in parallel with one another, one or both of the coils can beoperatively coupled to a load. As another example, when two coils areconnected in series, one of the coils can receive an input voltage andcan output an intermediate voltage to the input of the second coil, andan output of the second coil can be operatively coupled to a load.

In some embodiments, each of the coils can include one or more taps atdifferent location on the coil to allow the user of the resonanttransformer to obtain different output voltages and inductance valuesfrom the resonant transformer in response to the same input voltage. Anumber of turns between the input to the coil and the tap locations candetermine a voltage output at a given tap as well as an inductanceassociated with the coil.

Referring now to FIGS. 1A and 1B, an exemplary resonant transformer 100,in accordance with exemplary embodiments of the present disclosure, caninclude a magnetic core 120 having a first leg 126 and a second leg 130,and conductor coils or windings 150 and 160, which can be disposed,wound, or wrapped about the first and second legs 126 and 130 of thecore 120. In an exemplary operation, the core 120 can be electricallycoupled to ground. In exemplary embodiments, a core mandrel 170, shownin FIG. 1B, can surround the first and second legs 126 and 130 and thecoils 150 and 160 can be wound over at least the core mandrel 170 suchthat the core mandrel 170 is disposed between the core and the coils 150and 160. The resonant transformer 100 can be configured to have anadjustable inductance and to output high voltages (e.g., kilovolts, tensof kilovolts, hundreds of kilovolts) in response to an input voltage(e.g., an input voltage received by an exciter 102). In exemplaryembodiments, the coils 150 and 160 can include as many turns asnecessary to achieve a desired voltage at an output of the resonanttransformer 100. In some embodiments, the coils 150 and 160 can beelectrically coupled to each other in parallel or series as describedherein.

As shown in FIGS. 1A and 1B, the coil 150 can include taps 152 and 154,and the coil 160 can include taps 162 and 164. While coils 150 and 160have been illustrated as each including two taps, those skilled in theart will recognize that the coils 150 and 160 can include more or fewertaps. Each of the taps 152 and 154 can be electrically coupled to thecoil 150 at different locations on the coil 150, and each of the taps162 and 164 can be electrically coupled to the coil 160 at differentlocations on the coil 160. The different tap locations correspond to adifferent number of turns in the coil such that the resonant transformer100 can be configured to output different voltages at each tap inresponse to the same input voltage. Because the tap locations correspondto a different number of turns in the coils 150 and 160, an inductanceof the resonant transformer 100 associated with each of the taplocations on the coils can be different.

The coils 150 and 160 can be electrically coupled to each other inparallel (as illustrated by node “X”) such that each of the coils 150and 160 can receive the same input voltage and can generate separateoutput voltages in response to the input voltage. In exemplaryembodiments, the coils 150 and 160 can be formed to be substantiallysimilar or identical (e.g., can each include the same number of turnsusing the same type of wire), and the taps 152 and 162 can correspond tosubstantially identical tap locations on the coils 150 and 160 such thatwhen the taps 152 and 162 are used (for parallel coils 150 and 160), thecoils 150 and 160 can be configured to have substantially identicalinductances and to output substantially identical voltages in responseto the same input voltage. Likewise, the taps 154 and 164 can correspondto substantially identical tap locations on the coils 150 and 160 suchthat when the taps 154 and 164 are used (for parallel coils 150 and160), the coils 150 and 160 can be configured to have substantiallyidentical inductances and to output substantially identical voltages inresponse to the same input voltage.

In exemplary embodiments, when the coils 150 and 160 are connected inparallel, either of the coil 150 or 160, or both of the coils 150 and160, can be operatively coupled to a load (e.g., a capacitive load) in aresonant circuit. As one example, the tap 152 of the coil 150 can beoperatively coupled to the load, and the remaining taps can beelectrically isolated from the load. In this configuration, the outputvoltage of the resonant circuit 100 is determined based on the inputvoltage to the coil 150 and the number of turns in the coil 150 up tothe tap 152. As described herein, when only the coil 150 is operativelycoupled to the load, the inductance of the resonant transformer 100 canbe determined based on the number of turns in the coil up to the tap 152and based on a controllable gap in the core 120 of the resonanttransformer 100. As another example, the taps 152 and 162 can beoperatively coupled to the load in parallel, and the remaining taps canbe electrically isolated from the load. In this configuration, asdescribed herein, the output voltage at the taps 152 and 162 can besubstantially identical (e.g., where coils 150 and 160 are substantiallyidentical and the taps 152 and 162 are positioned at corresponding taplocations). As described herein, when both of the taps 152 and 162 ofcoils 150 and 160, respectively, are operatively coupled to the load inparallel, the inductance of the resonant transformer 100 can bedetermined based on the number of turns in the coil 150 up to the tap152, the number of turns in the coil 160 up to the tap 162, and acontrollable gap in the core 120 of the resonant transformer 100. Forexample, where the coils 150 and 160 are substantially identical, andthe taps 152 and 162 are positioned at corresponding tap locations, theinductance of the resonant transformer 100 when only the tap 152 is usedcan generally be twice the inductance of the resonant transformer 100when the taps 152 and 162 are used in parallel and the gap in the coreis the same. Using the coils 150 and 160 in parallel can allow theresonant transformer to operate at higher current ratings than using asingle coil because the output current is divide over the two coils.

In some embodiments, the resonant transformer 100 can be configured toelectrically couple the coils 150 and 160 in series such that the outputfrom the coil 150 forms the input to the coil 160. In thisconfiguration, where coils 150 and 160 are substantially identical, theoutput voltage of the resonant transformer can be as much as or morethan twice the output voltage of the coils 150 and 160 when used singlyor connected in parallel, and the inductance of the resonant transformer100 can be as much as or more than twice the output voltage of the coils150 and 160 when used singly or connected in parallel. In someembodiments, the resonant transformer 100 can be reconfigurable toswitch between a parallel and series arrangement of the coils 150 and160. To connect the coils 150 and 160 in series, the input to the coilcan be connect to node “X1” and node “A” can be connected to node “X2”such that an output of the coil 150 forms the input to coil 160.

Referring to FIG. 1B, the core 120 of the resonant transform can have aU/I configuration. The legs 126 and 130 can be formed by a (U-shaped)core segment 122 and can be positioned generally parallel to oneanother. The legs 126 and 130 can be coupled to each other at one end bya magnetic member 128, while the other terminal ends 132 and 136 of thelegs 126 and 130, respectively, are separated or spaced away from an(I-shaped) core segment 124 by one or more gaps 175 (e.g., air gaps).

The core segment 124 can have an elongate I-shaped body 140 including afirst end 142 and a second end 144. In some embodiments, the elongatebody 140 can extend linearly along its length between the first andsecond ends 142 and 144. In some embodiments, the elongate body can becurved along its length. A cross section of the body 140 takentransversely to a length of the body 140 can be rectangular. The firstend 142 of the body 140 is disposed proximate to the terminal end 132 ofthe first elongate portion 126 of the core segment 122 and the secondend 144 of the body 140 can be disposed proximate to the terminal end136 of the second elongate portion 128 of the core segment 124.

A position of the core segment 124 with respect to the core segment 122can be moved to adjust the size of the gap(s) 175 to increase ordecrease a distance between the core segment 124 the terminal ends 132and 136 of the legs 126 and 130; thereby adjusting an inductance of theresonant transformer 100. For example, the size of the gap(s) 175 can bedecreased to increase an inductance of the resonant transformer or canbe increased to decrease the inductance of the resonant transformer.

The size of the gap(s) 175 can be varied between a minimum value and amaximum value such that one or more ranges of inductance values can beachieved using the resonant transformer 100. As one example, where bothof the taps 152 and 162 of the coils 150 and 160, respectively, are usedin parallel with a load, the size of the gap(s) 175 can be controlled tooperate the resonant transformer 100 within a first range of inductancevalues. As another example, when only one of the taps of one of thecoils (e.g., tap 152 of coil 150) is used, the gap 175 can be controlledto operate the resonant transformer 100 within a second range ofinductance values (e.g., twice the inductance values of the firstrange). As yet another example, where both of the coils 150 and 160 areused in series with a load, and the tap 162 is used as an output of theresonant transformer 100, the size of the gap(s) 175 can be controlledto operate the resonant transformer 100 within a third range ofinductance values (e.g., twice the inductance values of the secondrange).

As a non-limiting example to illustrate an operation of exemplaryembodiments of the resonant transformers described herein, the coils 150and 160 can be electrically coupled in parallel and can include coilarrangements described herein having a specified number of turns togenerate a voltage upwards of, for example, forty (40) kilovolts inresponse to an input voltage of about two thousand (2,000) to fourthousand (4,000) kilovolts. The coil arrangement of the coils 150 and160 to achieve this output voltage can create an inductance in the coilthat allows the size of the gap to be relatively small when compared toconventional resonant transformers. For example, in some embodiments,when only the coils 150 is used the gap size can be varied fromapproximately one (1) millimeter to approximately fifty (50) millimetersto generate an inductance of approximately four hundred (400) Henries toapproximately thirty (30) Henries, respectively, while some conventionalresonant transformers generally require a maximum gap size ofone-hundred fifty (150) millimeters to achieve the lower end of theinductance range. When the coils 150 and 160 are used in parallel, thesame range for the size of the gap can be used to generate an inductanceof approximately two hundred (200) Henries to approximately fifteen (15)Henries, while allowing the current rating of the resonant transformerto approximately double. When the coils 150 and 160 are used in series,the same range for the size of the gap can be used to generate aninductance of approximately eight hundred (800) Henries to approximatelysixty (60) Henries.

FIGS. 2-5 depict a coil arrangement 200 of a resonant transformer andportions thereof in accordance with exemplary embodiments of the presentdisclosure. For example, exemplary embodiments of the coil arrangement200 can be used for embodiments of the conductor coils or windings 150and/or 160 disposed, wound, or wrapped about portions (e.g., legs) ofthe core segment 122, as described herein. FIG. 2 depicts an exemplarycross-section of an exemplary portion of the coil arrangement 200 takentransverse to a central axis 202 of the coil arrangement 200. FIG. 3depicts an exemplary cross-section of an exemplary portion of the coilarrangement 200 taken along the central axis 202 of the coil arrangement200.

Referring to FIGS. 2 and 3, the coil arrangement 200 can be coaxiallyand concentrically wrapped or wound over a non-metallic core mandrel 210that surrounds a magnetic core segment 205. The coil arrangement 200 caninclude coaxially and concentrically arranged layers of pressure tape,compressible insulating material, and conductive wire wound insuccessive layers over the core mandrel 210 in a generally repetitivepattern. In some embodiments, the pressure tape can be formed from Mylarand the compressible insulating material can be high voltageethylene-propylene rubber (EPR). In some embodiments, a (first) layer212 of an insulating material can substantially cover an outer surfaceof the core mandrel 210, and a (first) layer 214 of pressure tape can bedisposed coaxially and concentrically over the (first) layer 212 of theinsulating material.

A course 216 of grounding wire can be coaxially and concentricallywrapped or wound around the (first) layer 214 of the pressure tape alongthe portion of the length of the core mandrel 210 to form a coil havinga generally helically shape and a specified number of total turns. Thepressure tape generally prevents the turns of coils from individuallyindenting the insulating material such that coils uniformly compress theinsulating material. In some embodiments, the grounding wire can bewrapped directly on the core mandrel 210. The course 216 of groundingwire can form a grounding coil of the coil arrangement 200 and can bewrapped or wound such that the grounding coil provides a net-zeroinduced voltage measured between a first end of the course 216 and asecond end of the course 216. A first end of the grounding wire can beoperatively coupled to ground at the first end of the mandrel and asecond end of the grounding wire can be a free or “floating” end (e.g.,not directly or indirectly electrically coupled to ground or anothervoltage potential).

Still referring to FIGS. 2 and 3, a (second) layer 218 of the pressuretape can be disposed over the course 216 of grounding wire tosubstantially cover the course 216 of the grounding wire, and a (second)layer 220 of the compressible insulating material can be disposed overthe (second) layer 218 of the pressure tape to substantially cover the(second) layer 218 of the pressure tape. A (third) layer 222 of thepressure tape can be disposed over the (second) layer 220 of thecompressible insulating material to substantially cover the (second)layer 220 of the compressible insulating material. In some embodiments,the layers 212, 214, 216, 218, 220, and 222 can be referred to as thegrounding coil layer of the core arrangement 200.

The layers that are added to the core arrangement 200 after (orincluding) the (third) layer 222 of the pressure tape can form arepetitive pattern. Although two iterations of the repetitive patternare described with respect in FIGS. 2 and 3, exemplary embodiments ofthe present disclosure can include more or fewer iterations of therepetitive pattern. For example, the pattern can be repeated, asnecessary, to achieve a specified or desired inductance or outputvoltage with the resonant transformer. A first iteration of therepetitive pattern can include a (first) course 224 of step-up wire thatcan be coaxially and concentrically wrapped or wound around the (third)layer 222 of the pressure tape along the portion of the length of thecore mandrel 210 to form a coil having a generally helically shape and aspecified number of total turns. The pressure tape generally preventsthe turns of coils from individually indenting the insulating materialsuch that coils uniformly compress the insulating material. A first endof the (first) course 224 of coil can be connected to an input node ofthe resonant transformer or to an output of another coil in the resonanttransformer. The (first) course 224 of step-up wire can form a voltagestep-up coil of the coil arrangement 200 and can be wrapped or woundsuch that a non-zero voltage can be generated in the step-up coil (e.g.,at a second end or anywhere along the length of the step-up coil) inresponse to an input voltage received at a first end of the step-upwire.

A (fourth) layer 226 of the pressure tape can be disposed over the(first) course 224 of the step-up wire to substantially cover the(first) course 224 of the step-up wire, and a (third) layer 228 of thecompressible insulating material can be disposed over the (fourth) layer226 of the pressure tape to substantially cover the (fourth) layer 226of the pressure tape. A (fifth) layer 230 of the pressure tape can bedisposed over the (third) layer 228 of the compressible insulatingmaterial to substantially cover the (third) layer 228 of thecompressible insulating material. In some embodiments, the layers 224,226, 228, and 230 can be referred to as a (first) step-up coil layer ofthe core arrangement 200.

To illustrate the repetitive pattern, a second iteration of therepetitive pattern is shown to include a (second) course 232 of thestep-up wire that can be coaxially and concentrically wrapped or woundaround the (fifth) layer 230 of the pressure tape along the portion ofthe length of the core mandrel 210 to form a coil having a generallyhelically shape and a specified number of total turns that is less thanthe number of turns of the preceding step-up coil. The (second) course232 of wire is a continuation of the step-up wire used to form precedingstep-up coil (or is electrically coupled to an end of the step-up wireused to form the preceding step-up coil). The pressure tape generallyprevents the turns of coils from individually indenting the insulatingmaterial such that coils uniformly compress the insulating material. The(second) course 232 of wire can form another voltage step-up coil of thecoil arrangement 200.

A (sixth) layer 234 of the pressure tape can be disposed over the(second) course 232 of the wire to substantially cover the (second)course 232 of the wire, and a (fourth) layer 236 of the compressibleinsulating material can be disposed over the (sixth) layer 234 of thepressure tape to substantially cover the (sixth) layer 234 of thepressure tape. A (seventh) layer 238 of the pressure tape can bedisposed over the (fourth) layer 236 of the compressible insulatingmaterial to substantially cover the (fourth) layer 236 of thecompressible insulating material. In some embodiments, the layers 232,234, 236, and 238 can be referred to as a (second) step-up coil layer ofthe core arrangement 200.

As shown in FIGS. 2 and 3, each step-up coil layer in the coilarrangement 200 can be formed sequentially by coaxially andconcentrically wrapping or winding a course of step-up wire around aprevious coil layer (e.g., a previous step-up coil layer or a groundingcoil layer) along at least a portion of a length of the core mandrel210. The coil in the grounding coil layer can be wrapped or wound aboutat least a portion of the length of the core mandrel 210 such that thereare no coil layers between the grounding coil layer and the core mandrel210. In exemplary embodiments, the coil layers of the core arrangement200 (e.g., step-up coil layers and a grounding coil layer) and the coremandrel 210, can each be generally disposed coaxially and concentricallywith respect to each other.

A quantity of step-up coil layers in the coil arrangement 200 candetermine an output voltage that is output by a resonant transformer(e.g., embodiments of the transformers described herein) in response toan input voltage. In exemplary embodiments, each successive/consecutivestep-up coil layer can include fewer turns than the preceding step-upcoil layer to form a stepped or graded geometry of step-up coil layershaving an generally sloping profile at the ends of the coil arrangement200, as shown in FIG. 3. A total number of cumulative turns in thestep-up coil layers can be specified to achieve a desired output voltagein response to a specified input voltage. The stepped or gradedstructure of the coil arrangement can provide electrical stability tothe coil arrangement to reduce or mitigate undesirable discharges forthe coil arrangement during use. In exemplary embodiments, the quantityof step-up coil layers can be selected for generating a high voltage(e.g., the quantity of step-up coil layers can be selected to generatehundreds of volts, kilovolts, tens of kilovolts, hundreds of kilovolts)in response to a moderate input voltage (e.g., kilovolts). As anon-limiting example, in some embodiments, the coil arrangement 200 canbe configured to receive an input voltage of approximately zero (0) toapproximately two (2) kilovolts, and can be configured to outputapproximately zero (0) to forty (40) kilovolts.

FIG. 4 is a schematic diagram of an exemplary winding of the course 216of the grounding wire to form a grounding coil 400 for the coilarrangement 200. The course 216 of wire can be wrapped or wound aboutthe core mandrel to achieve a net-zero induced voltage measured betweenthe first end and the second end of the grounding coil 400 formed by thecourse 216 of grounding wire. To achieve the net-zero induced voltage,the grounding wire is wound such that a total number of turns of thegrounding coil in the clockwise direction along the length of the coremandrel 210 is equal to or substantially equal to a total number ofturns in the counter clockwise direction along the length of the coremandrel for the course 216 of grounding wire. For example, half of theturns for the course 216 of grounding wire (i.e., forming the groundingcoil) can be in the clockwise direction and half of the turns for thecourse 216 of grounding wire can be in the counter clockwise direction.

To reduce voltage build-up within the grounding coil, a direction inwhich the course 216 of grounding wire is wrapped or wound can alternate(e.g., between clockwise and counterclockwise directions about the coremandrel). For example, in exemplary embodiments, the course 216 of wire(i.e. the grounding coil) can be wrapped or wound so that the wirealternates between a specified number of turns about the core mandrel210 in a first generally circumferential direction along a length of thecore mandrel 210 as shown by arrow 402 (e.g. a specified number of turnsin a clockwise direction) and a specified number of turns about the coremandrel 210 in a second circumferential direction along a length of thecore mandrel as shown by arrow 404 (e.g. a specified number of turns ina counter clockwise direction). As shown in FIG. 4, for example, thecourse 216 of grounding wire can be wrapped and wound about the coremandrel 210 to alternate between the same number of turns in theclockwise and counterclockwise directions (e.g., alternating between tenturns in the clockwise direction and ten turns in the counter clockwisedirection). While FIG. 4 illustrates a non-limiting example of a patternof alternating turns that form the grounding coil, exemplary embodimentsof the present disclosure can be implemented using other patterns ofalternating turns so that the wire is wound to form a grounding coilthat has an equal or substantially equal number of turns in theclockwise direction along the length of the core mandrel 210 and in thecounter clockwise direction along the length of the core mandrel 210 forthe (first) course 216 of the grounding wire.

FIG. 5 shows an electrical stress control arrangement that can beimplemented for the coil arrangement 200. As shown in FIG. 5, gradingtape 502 can be disposed along the sloped profile of the stepped orgraded ends of the coil arrangement 200 to limit the electrical stresson the coil arrangement 200 at the ends of the coil arrangement 200. Thegrading tape 502 can be inserted between step-up coil layers and canextend generally towards the core mandrel 210. As the grading tape 502approaches the core mandrel 210, the grading tape can be bent totransition from a generally radial direction to a generally longitudinaldirection with respect to the core mandrel. The grading tape 502 can bedisposed with respect to the core mandrel 210 such that the grading tape502 is in proximity to, but does not come in contact with the groundcoil (e.g., is spaced away from the ground coil by, for example,approximately one centimeter). The grading tape 502 can be formed of anon-linear dielectric material that limits the electrical stress at theends of the coil arrangement 200 to prevent or reduce undesirableelectrical discharges or breakdowns at the ends of the coil arrangement200. For example, in some embodiments, the grading tape 502 can beformed by a polymer base, such as EPR rubber, with ferroelectric ormetal oxide powdered materials to impart dielectric non-linearity to thegrading tape 502.

In exemplary embodiments, pieces of the grading tape 502 can be layeredand stacked radially from the grounding coil to an outer step-up coillayer. For example, a first piece of grading tape 510 can extend fromproximate to grounding coil up to a specified number of step-up coils. Asecond piece of pressure tape 520 can begin at and overlap the end ofthe first piece of grading tape 510 and can extend up to a specifiednumber step-up coil layers. A third piece of grading tape 530 can beginat and overlap the end of the second piece of grading tape 510 and canextend up to a specified number step-up coil layers. In general, thegrading tape 502 is disposed to cover the edge of the coil arrangement200 and extend to be proximate to the grounding coil to limit or relieveelectrical stress that may build up at the ends of the coil arrangement200.

Embodiments of the coil arrangement 200 described with respect to FIGS.2-5 can advantageously reduce the likelihood of undesirable electricaldischarges due to the configuration of the grounding coil layer, thepressure tape layers, the insulating material layers, the use of fewerturns on successive layers of step-up coil to create a sloped profile,and/or the use of the grading tape along the ends of the coilarrangement. The reduction of the likelihood of undesirable electricaldischarge advantageously allows exemplary embodiments of the resonanttransformers that utilize the coil arrangement 200 to operate safely andeffectively without require the coil arrangement for be immersed in aninsulating oil. As a result, exemplary embodiments of the presentdisclosure can include resonant transformers that are lighter thanconventional resonant transformers. The reduced likelihood ofundesirable electrical discharges also allows the coil arrangement 200to include more turns than coils in convention resonant transformers,which allows exemplary embodiments of the resonant transformers to havehigher inductances and higher output voltages than convention resonanttransformers. By creating coils according the embodiments of the coilarrangement 200 with higher inductances than conventional coilarrangements, the size of gap in exemplary embodiments of resonanttransformers described herein can be smaller than conventional resonanttransformers, while allowing for a wide range of inductances suitablefor achieving resonance with a wide range of load capacitances.

FIG. 6 depicts an exemplary main housing 600 within which is housed atleast a portion of an embodiment of the resonant transformer 100 havingcoils 150 and 160 (FIGS. 1A-B) formed according to embodiments of thecoil arrangement 200 (FIGS. 2-5). For example, in some embodiments, thecore segments 122 and 124 (FIGS. 1A-B) can be disposed within thehousing 600 or the core segment 122 can be disposed within the housing600 and the core segment 124 can be disposed external to the housing600. The housing 600 can have a width W, a depth D, and a height H. Insome embodiments, a volume of the housing can be less than approximately25,000 cubic inches due to the structure of the coil arrangement as wellas the positioning of the core segments and the maximum size of the gapneed to produce an inductance suitable for testing electrical powercables of different lengths. As shown in FIG. 6, a wall 610 of thehousing 600 can include one or more bushings (or ports) 612 throughwhich the taps 152, 154, 162, and 164 can be accessed to configure theresonant transformer to connect an input voltage to the resonanttransformer 100 and to connect a load to one or more of the taps 152,154, 162, and/or 164.

In exemplary embodiments, because the coil arrangement 200 of the coils150 and 160 can be configured to reduce and/or minimize undesirabledischarge of the coils 150 and 160, exemplary embodiments of the presentdisclosure do not generally require that an interior of the main housing600 be filled with an insulating oil. The main housing 785 can be sealedto maintain a gas under a low to moderate pressure (e.g., approximately0 to approximately 5 psig). Because the coil arrangement allows theinterior of the housing 600 to be filled with air or an inert gas,rather than an insulting oil, exemplary embodiments of the resonanttransformers described herein can be lighter than conventional resonanttransformers. By positioning the core segment 124 and gap 175 (FIGS.1A-B) outside of the housing 600, an interior volume of the housing 600can be reduced in comparison to conventional resonant transformers. Thecombination of the coil arrangement and the position of the core segment124 external to the housing 600 provides for a smaller, lighter,efficient, and stable variable inductance resonant transformer ascompared to conventional resonant transformers.

FIGS. 7-10 depict various exemplary embodiments of resonant transformersin accordance with the present disclosure.

FIGS. 7A depicts a schematic diagram of the resonant transformer 700where the core segment 124 is disposed externally to a housing 785 andis operatively coupled to the housing 785 by a joint 746 (e.g., a hinge)in accordance with exemplary embodiments of the present disclosure. Asshown in FIG. 7A, the resonant transformer can include the U/I-shapedmagnetic core 120 formed by the core segment 122 and the core segment124, and the conductor coils or windings 150 and 160 disposed, wound, orwrapped over the core mandrels disposed on the legs 126 and 130 of thecore segment 122 according to embodiments of the coil arrangementdescribed herein. In some embodiments, the resonant transformer 700 caninclude only one of the coils 150 or 160, as shown in FIG. 7B.

A spatial relationship between the core segment 122 and the core segment124 can be adjustable to adjust an inductance of the resonanttransformer. As shown in FIGS. 7A and 7B, a distance between the secondend 144 of the core segment 124 and terminal end 136 of the second leg130 of the core segment 122 remains generally constant and a distancebetween the first end 142 of the core segment 124 and the terminal end132 of the first leg 126 of the core segment 122 can be varied tocontrol an inductance of the resonant transformer. In some embodiments,the second end 144 can be disposed proximate to the terminal end 136,but not in contact with the terminal end 136 such that substantiallyfixed gap exists between the second end 144 and the terminal end 136.

In exemplary embodiments, the second end 144 can be operatively coupledto the terminal end 136 the housing 785 via a joint 746 formed by, forexample, a hinge, a ball and socket joint, ratchet mechanism, and/or anyother suitable pivoting or rotating structure. The first end 142 of thecore segment 124 can be moved away from or towards the terminal end 132by operation of the joint 746 (e.g., between a first position and asecond position). As one example, the first end 142 can be moved to bepositioned proximate to terminal end 132 to define a minimum gap size orcan be moved away from (or further away from) the terminal end 132 toincrease the size of the gap 175 (e.g., to a maximum gap size or anintermediate gap size) and adjust the inductance of the resonanttransformer 700.

In some embodiments, the resonant transformer 700 can include aninflatable member 748 that can be positioned in the gap 175 between theterminal end 132 and the first end 142, as shown in FIG. 7C, such thatthe inflatable member 748 can be inflated to fill or at least partiallyfills the gap 175. The inflatable member 748 can be inflated such thatit presses against the core segment 124 and the core segment 124compresses the inflatable member 748 at an interface between the coresegment 124 and the inflatable member 748. In exemplary embodiments, theinflatable member 748 can provide mechanical stability to resonanttransformer by filling the gap 175 to prevent or reduce undesirablemovement of the core segment 124 with respect to the terminal end 132 ofthe core segment 122 due to, for example, vibrations or other mechanicalshocks. In some embodiments, the movement of the core segment 124 aboutthe joint 746 can be controlled manually by a user. In some embodiments,the movement of the core segment about the joint 746 can be controlledautomatically by an actuator. While exemplary embodiments have beenillustrated herein using inflatable members, exemplary embodiments ofthe present disclosure can use solid non-magnetic wedge-shaped membersinstead of or in addition to the inflatable members to provide stabilityto the resonant transformers by inserting the non-magnetic solid membersinto the space between the core segments.

In exemplary embodiments, an actuator 780 can be operatively coupled tothe core segment 124 to move the core segment 124 about the joint 746.For example, as shown in FIGS. 7A-7C, the actuator 780 can beoperatively coupled to the first end 142 of the core segment 124 tocontrol a distance (e.g., the gap 175) between the first end 142 and theterminal end 132; thereby controlling the inductance of the resonanttransformer 700. In some embodiments, the actuator 780 can be ascrew-type actuator in which a threaded shaft 782 operative coupled tothe core segment 124 rotates to move the core segment towards or awayfrom the core segment 122. The actuator 780 can be disposed inside oroutside of the housing 785.

In some embodiments, the actuator 780 can be manually and/orprogrammatically controlled to adjust the inductance of the resonanttransformer to a specified value. As one example, in some embodiments, acontrol interface 786 including one or more controls (e.g., buttons,knobs, etc.) can be operatively coupled to the actuator to allow a userof the resonant transformed to control the actuator 780. As anotherexample, in some embodiments, a processing device 784 (e.g.,microprocessor, microcontroller etc.) can be operatively coupled to theactuator 780 and can be programmed and/or configured to automaticallyand/or programmatically control the actuator 780 to control aninductance of the resonant transformer 700 based on a distance betweenthe first end 142 and the terminal end 132 in response to user inputsand/or in response to sensed and/or monitored parameters from which adesired inductance of the resonant transformer 700 can be derived.

As shown in FIG. 7A, the core segment 122, coil 150, and coil 160 can bedisposed within the main housing 785, while the core segment 124 candisposed outside of the main housing 785. The main housing 785 caninclude a barrier or wall 702 disposed between the core segments 122 and124 to position the gap 175 outside of the housing. By positioning thecore segment 124 (and the gap 175) outside of the main housing 785,exemplary embodiments of the present disclosure can substantially reducethe dimensions of the main housing as compared to tank housings ofconventional resonant transformers that are suitable for producing highvoltages (e.g., tens or hundreds of kilovolts), which can result in asmaller and lighter resonant transformer than conventional resonanttransformer designs. The core segment 124 can be exposed to theatmosphere at atmospheric pressure. In some embodiments, the coresegment 124 can be disposed within a secondary housing or shroud. Whilethe core segment 124 is described as being external to the main housing785, the core segment 124 of exemplary embodiments of the resonanttransformers described herein can be disposed within the housing.

In exemplary embodiments, the coil arrangement of the coils 150 and 160can be configured as described herein with respect to FIGS. 2-5 toreduce and/or minimize undesirable discharge of the coils 150 and 160such that exemplary embodiments of the present disclosure do notgenerally require that the interior of the main housing be filled withan insulating oil. In the present embodiment, the interior of the mainhousing 785 can be filled with a gas at atmospheric or moderatepressure. For example, the interior of the main housing 785 can befilled with air (e.g., atmosphere) or an inert gas (such as nitrogen).The main housing 785 can be sealed to maintain the gas 790 under a lowto moderate pressure (e.g., ˜0 to ˜5 psig). The wall 702 can be formedfrom a non-conductive, non-magnetic material. For example, in someembodiments, the wall 702 can be formed from Plexiglas, fiberglass,acrylic, plastic or other polymers, carbon-based composite materials,and/or any other suitable materials.

Because the coil arrangements described herein allow the interior of thehousing 785 to be filled with air or an inert gas, rather than aninsulting oil, exemplary embodiments of the resonant transformersdescribed herein can be lighter than conventional resonant transformers.The combination of the coil arrangement and the position of the coresegment 124 external to the housing 785 provides for a smaller, lighter,efficient, and stable variable inductance resonant transformer. Whilethe cores segment 124 has been described as being external to thehousing in some embodiments, those skilled in the art will recognizethat the core segment 124 can be disposed within the housing 785 whilestill realizing some advantageous of exemplary embodiments of thepresent disclosure as compared to convention resonant transformerdesigns.

FIGS. 8A and 8B are schematic diagrams of a resonant transformer 800 inaccordance with exemplary embodiments of the present disclosure. Theresonant transformer 800 can include embodiments of the magnetic core120 formed by the core segment 122 and the core segment 124, theconductor coils or windings 150 and 160 disposed, wound, or wrapped overthe core mandrel 170 disposed on the legs 126 and 130 of the coresegment 122, and the main housing 785 within which the core segment 122,coils 150 and 160, and gas 790 are disposed, as described herein. FIG.8A shows the first and second ends 142 and 144 of the core segment 124positioned to be proximate to the terminal ends 132 and 136 of the coresegment 122, respectively (e.g., spaced away from the terminal ends 132and 136 by a minimum distance D_(g1)). FIG. 8B shows the first andsecond ends 142 and 144 of the core segment spaced away from theterminal ends 132 and 136 of the core segment 122 by a maximum distanceD_(g2) to increase the size of gaps 802 and 804, respectively. In someembodiments, the resonant transformer 800 can include non-magneticinflatable members 848 that can be positioned in the gaps 802 and 804,as shown in FIG. 8C, such that the inflatable members 848 can beinflated to at least partially fill the air gaps 802 and 804 of theresonant transformer 800. In some embodiments, the resonant transformer800 can include one of the coils 150 or 160.

As shown in FIGS. 8A and 8B, both the first and second ends 142 and 144of the core segment 124 can be moved linearly and uniformly away ortowards the core segment 122. For example, a guide member 810 can bedisposed at each of the first and second ends 142 and 144 of the coresegment 124, and can be configured to engage a corresponding track 820that is mounted to and extends substantially perpendicularly away fromwall of the main housing 785. The actuators 780 can be operativelycoupled to the wall and the core segment 124, and can be actuated tomove the core segment 124 towards and away from the wall. As theactuators 780 translate the core segment 124, the guide member 810 ateach of the first and second ends 142 and 144 slide along thecorresponding track 820 so that the core segment 124 translates alonethe tracks 820 and can be positioned to be in contact with the terminalends 132 and 136 or spaced away from the terminal ends 132 and 136 toadjust the inductance of the resonant transformer 800.

FIG. 9 is a schematic diagram of a resonant transformer 900 inaccordance with exemplary embodiments of the present disclosure. Theresonant transformer 900 can include embodiments of the magnetic core120 formed by the core segment 122 and the core segment 124, theconductor coils or windings 150 and 160 disposed, wound, or wrapped overthe core mandrels 170 disposed on the legs 126 and 130 of the coresegment 122. As shown in FIG. 9, the core segments 122 and 124 of thecore 120 can be permanently connected or integrally formed, and a sliceof magnetic material that forms the core segment 124 can be removed fromthe core segment 124 to form a notch 995 in the core segment 124 that isdevoid of magnetic material. The size of the notch 995 can correspond toa maximum size of a gap 902. The core segments 122 and 124 can bedisposed in a housing 985, which can be filled with the gas 790 and arecess 975 can be formed in a wall 992 of the housing 985 and can extendinto the notch 995. The recess 975 in the housing can coincide with thenotch 995 and can have a width W_(N). The recess 975 can be configuredto receive the plunger insert 910. The dimensions of the plunger insert910 can correspond the recess 975 such that the plunger insert 910 fitscompletely and tightly or snugly within the recess 975 to fill the notch995. To achieve a variable inductance, plunger insert 910 can beinserted and/or removed from the recess 975. An actuator 980 can beoperatively coupled to the plunger insert 910 to control a movement ofthe plunger insert 910.

The plunger insert 910 can be formed by a tapered or wedge-shapedmagnetic portion 912 composed of a magnetic material and a tapered orwedge shaped non-magnetic portion 914 composed of a non-magneticmaterial. As shown in FIG. 9, the plunger insert 910 can have arectangular body that extends along a longitudinal axis L of the plungerinsert 910. The body can have a width W_(b) measured perpendicularly tothe longitudinal axis L, the portion 912 can have a width W_(MP), andthe portion 914 can have a width W_(NP). The width W_(b) of the body canbe slightly smaller than the width W_(N). The mathematical sum of thewidth W_(MP), and the width W_(NP) at any point along longitudinal axisL of the body can equal the width W_(b) of the body at such point. Inexemplary embodiments, at a first end of the body, the width W_(MP) ofmagnetic portion can be approximately equal to the width W_(b) of thebody, and at a second end of the body, the width W_(MP) of magneticportion can be approximately zero. At the first end of the body, thewidth W_(NP) of non-magnetic portion can be approximately zero, and atthe second end of the body, the width W_(NP) of magnetic portion can beapproximately equal to the width W of the body. In some embodiments, thewidth W_(MP) of magnetic portion can decrease linearly from the firstend to the second end, and the width W_(NP) of non-magnetic portion canincrease linearly from the first end to the second end. In someembodiments, the width W_(MP) of magnetic portion and the width W_(NP)of non-magnetic portion can change non-linearly along the longitudinalaxis L.

The actuator 980 can be operatively coupled to the plunger insert 910 tomove the plunger insert 910 into and out of the recess 975 to adjust thesize of the gap 902, and therefore, the inductance of the resonanttransformer 900. For example, the plunger insert 910 can be controlledby the actuator 980 to position the plunger insert 910 so that themagnetic portion 912 is disposed in the notch 995. The width W_(MP) ofthe magnetic portion 912 of the plunger insert 910 can determine theinductance of the resonant transformer 900. As one example, when thewidth W_(MP) of the magnetic portion 912 that is substantially equal tothe width W_(b) of the body is disposed in the notch, the size of thegap 902 can be reduced by the width W_(MP) of the magnetic portion 912disposed in the recess 975 and the inductance of the resonanttransformer will be at its maximum value. As another example, when themagnetic portion 912 of the inert 910 is removed from the recess 975,the size of gap 902 can be at its maximum and the inductance of theresonant transformer will be at its minimum value. Thus, the widthW_(MP) the magnetic portion 912 can be used to change a width of the gap902 to change the inductance of the resonant transformer 900.

FIGS. 10A and 10B are schematic diagrams of a resonant transformer 1000in accordance with exemplary embodiments of the present disclosure. Theresonant transformer 1000 can include embodiments of the magnetic core120 formed by the core segment 122 and the core segment 124, theconductor coils or windings 150 and/or 160 disposed, wound, or wrappedover the core mandrels 170 disposed on the legs 126 and 130 of the coresegment 122, the guide member(s) 810, the track(s) 820, the main housing785 within which the core segment 122, coils 150 and 160, and gas 790are disposed, as described herein.

As shown in FIGS. 10A and 10B, the first and second ends 142 and 144 ofthe core segment 124 can be moved linearly and uniformly away from ortowards the core segment 122. A non-metallic solid or inflatable insertis squeezed between the core segments 122 and 124 to control the gapsize and prevent vibrations.

One or more resilient members 1020 (e.g., springs) can be operativelycoupled between the core segment 124 and the wall 702. The resilientmember 1020 can be biased to urge the core segment 124 towards the wall702 and to force the core segment 124 to be in contact with or proximateto the core segment 122 when the inflatable members 1010 are in thefirst state (e.g., substantially deflated so that the core segment 124is in contact with the core segment 122). In exemplary embodiments, theresilient members 1020 can exert a force F1 on the core segment 124 inthe direction shown by arrow 1022, while the inflatable inserts exert aforce in the opposite direction, tending to increase the size of thegap.

One or more actuators 1080 (e.g., pumps) can be operatively coupled tothe inflatable members 1010, and can be operated to inflate and/ordeflate the inflatable members 1010. When the actuators 1080 areoperated to inflate the inflatable members 1010, the inflatable members1010 can exert a force F2 on the core segment 124 in a directionopposite that of the force F1 exerted on the core segment 124 by thespring 1020 (as shown by arrow 1024). As the inflatable members 1010 areinflated, the force F2 exerted on the cores segment 124 increases. Whenthe force F2 is greater than the force F1, the inflatable members 1010urge the core segment 124 away from the wall 702 and the core segment122. A distance between the core segments 124 and 122 can be controlledby controlling a degree to which the inflatable members 1010 areinflated. For example, when the inflatable members 1010 aresubstantially deflated, the core segment 124 can be proximate to thecore segment 122 to define a minimum distance between the segments 122and 124; when the inflatable members 1010 are fully inflated, the coresegment 124 can be spaced away from the core segment 124 by a maximumdistance between the segments 122 and 124; and when the inflatablemembers 1010 are inflated half way, the inflatable members 1010 canposition the core segment 124 at a distance that is approximately halfthe maximum distance.

By adjusting a distance between the core segment 124 and the coresegment 122 using the inflatable members 1010 and the springs 1020, theinductance of the resonant transformer 1000 can be adjusted. The forceF1 exerted on the core segment 124 by the spring 1020 and the force F2exerted on the core segment 124 by the inflatable members can be intension and can operate to stabilize the core segment 124 (e.g., inhibitundesirable movement of the core segment due to, for examplevibrations). Limiting undesirable movement of the core segment 124during an operation of the transformer 1000 can advantageously allow thetransformer to provide a substantially stable, accurate, and preciseinductance value.

Exemplary embodiments of the present disclosure advantageously provide arelatively small and light resonant transformer that can be controlledto provide an accurate and stable inductance value. For example,embodiments of the coil arrangement described herein can reduceundesirable electrical discharges to provide a stable resonanttransformer that can operate without being enclosed in a housing that ismaintained under high pressure or filled with oil as are conventionalhigh voltage resonant transformers. Unlike conventional resonanttransformers, which use cellulose and an insulating oil to maintaindielectric stability, the (dielectric) stability provided by embodimentsof the coil arrangement, allows the housing of exemplary embodiments ofthe resonant transformer (when used) to be filled with lightermaterials, such as air at low humidity (dry air) or inert gases (e.g.,nitrogen) at relatively low pressure (0-5 psig). Additionally, bydisposing a portion of the split magnetic core external to the mainhousing, the main housing can be made smaller than tanks of conventionaltransformers, which advantageously provide for a further reduction insize and weight as compared to convention resonant transformers.Experimental data indicates that exemplary embodiments of the resonanttransformer can have a total weight (including power supply andcontrols) that is less than approximately thirty-five percent (35%) toapproximately sixty-five percent (65%) of the weight of an equivalentconventional resonant transformer. A reduction in size and weight of theresonant transformer can allow exemplary embodiments of the resonanttransformer to be housed inside a small van rather than a medium sizetruck.

When the air gap is set to a minimum value, exemplary embodiments of theresonant transformers described herein can generate an inductance thathas a value that significantly higher than conventional resonanttransformers; allowing resonance to be achieved with very short cables.For example, due to the dielectric stability of the coil arrangementsdescribed herein, the coils of the resonant transformers can include anumber of turns to generate a large enough inductance to form a resonantcircuit with a load capacitance of ten (10) to twenty (20) nanofarads.Such inductances are typically not achieved at power frequencies of 50Hz to 60 Hz in commercially available conventional resonanttransformers.

Similarly, the air gaps of exemplary embodiments of the resonanttransformers of the present disclosure can advantageously be smallerthan that in a conventional resonant transformer and can be configuredin such a manner that the air gap can be placed either outside or insidethe main housing. Because the coil arrangements described herein cangenerate a suitably large inductance while maintaining dielectricstability, the size of the gaps can be reduced as compared toconventional resonant transformers, while still achieve a wide range ofinductances to allow the resonant transformer to be configured toachieve resonance with small load capacitances (e.g., 10 nanofarads) andlarge load capacitances (e.g., 800 nanofarads). The size of the air gapcan be changed step-wise or continuously with the possibility ofinserting a non-magnetic spacer between the faces of a split magneticcore and by exerting a compressive force on the inserts, to obtain areactor inductance falling very close to that required to achieveresonance with the capacitance of the test cable. Final resonance can beachieved by changing a frequency of an input voltage to the resonanttransformer between, for example, 50 Hz and 60 Hz.

The advantages over conventional resonant transformers described hereinare not exhaustive. These and other advantages will be recognized by oneskilled in the art upon consideration of exemplary embodiments of thepresent disclosure.

In describing exemplary embodiments, specific terminology is used forthe sake of clarity. For purposes of description, each specific term isintended to at least include all technical and functional equivalentsthat operate in a similar manner to accomplish a similar purpose.Additionally, in some instances where a particular exemplary embodimentincludes a plurality of system elements, device components or methodsteps, those elements, components or steps may be replaced with a singleelement, component or step. Likewise, a single element, component orstep may be replaced with a plurality of elements, components or stepsthat serve the same purpose. Moreover, while exemplary embodiments havebeen shown and described with references to particular embodimentsthereof, those of ordinary skill in the art will understand that varioussubstitutions and alterations in form and detail may be made thereinwithout departing from the scope of the invention. Further still, otherembodiments, functions and advantages are also within the scope of theinvention.

1. A resonant transformer comprising: a magnetic core; a core mandrelwrapped over a leg of the magnetic core; and a coil having a coilarrangement wrapped coaxially and concentrically over the core mandrel,the coil arrangement includes: a grounding coil layer configured toprovide a net-zero induced voltage between opposite ends of the groundcoil layer; and a plurality of step coil layers, the plurality of stepcoil layers being wound coaxially and concentrically about the groundingcoil layer, wherein each successive step-up coil layer in the pluralityof step-up coil layers includes fewer turns than a preceding step-upcoil lay in the plurality of step-up coil layers.
 2. The resonanttransformer of claim 1, wherein each end of the coil arrangementincludes grading tape to control an electrical stress along each end ofthe coil arrangement.
 3. The resonant transformer of claim 1, whereinthe grounding coil layer includes a grounding coil alternating between aspecified number of turns in a first direction and the specified numberof turns in a second direction.
 4. The resonant transformer of claim 3,wherein a total number of turns in the first direction equals a totalnumber of turns in the second direction between a first end and a secondend of the grounding coil.
 5. The resonant transformer of claim 1,wherein the grounding coil layer comprises a grounding coil sandwichedbetween two layers of pressure tape.
 6. The resonant transformer ofclaim 1, wherein at least one of the step-up coil layers comprises: astep-up coil; a layer of pressure tape covering the step-up coil; anlayer of insulating material covering the layer of pressure tape; and afurther layer of pressure tape covering the layer of insulatingmaterial.
 7. The resonant transformer of claim 1, further comprising: ahousing, at least the leg of the magnetic core, the core mandrel, andthe coil are disposed within the housing.
 8. The resonant transformer ofclaim 7, wherein the housing is filled with air or an inert gas.
 9. Theresonant transformer of claim 7, wherein the magnetic core includes afirst core segment that includes the leg and a second core segment thatis spaced away from the first core segment to define a gap that isdevoid of a magnetic material.
 10. The resonant transformer of claim 9,wherein a size of the gap is adjustable to change an inductance of theresonant transformer.
 11. The resonant transformer of claim 7 wherein agap is formed in the magnetic core and a size of the gap is adjustableto change an inductance of the resonant transformer.
 12. A coilarrangement for a transformer comprising: a grounding coil woundconcentrically about and spaced away from a magnetic core of atransformer, the grounding coil being wound in alternating directionsalong a portion of the magnetic core to generate an induced voltagebetween a first end of the ground coil and a second end of the groundingcoil that is substantially zero.
 13. The coil arrangement of claim 12,wherein the grounding coil is wound a first number of turns in firstcircumferential direction about the magnetic core and wound a secondnumber of turns in a second circumferential direction about the magneticcore.
 14. The coil arrangement of claim 13, wherein the first number ofturns is disposed adjacent to the second number of turns.
 15. The coilarrangement of claim 13, wherein the first number of turns equals thesecond number of turns.
 16. The coil arrangement of claim 12, furthercomprising: a first layer of insulating material disposed concentricallyabout a portion of a magnetic core of a transformer and sandwichedbetween layers of pressure tape, the grounding coil wound concentricallyabout and spaced away from a magnetic core of a transformer by at leastthe first layer of insulating material and the layers of pressure tape;a second layer of insulating material disposed concentrically over thegrounding coil and sandwiched between further layers of pressure tape.17. A coil arrangement for a transformer comprising: a step-up coillayer that includes: a course of wire wound concentrically about andspaced away from a magnetic core of a transformer; a layer of pressuretape disposed concentrically over the course of wire; a layer ofinsulating material disposed circumferential over the layer of pressuretape; and a further layer of pressure tape disposed concentrically overthe layer of insulating material.
 18. The coil arrangement of claim 17,further comprising: a further step coil layer disposed circumferentialand coaxially over the step-up coil layer, the further step-up coillayer, the further step-up coil layer including: a further course ofwire wound concentrically about the further layer of pressure tape, thefurther course of wire compressing the layer of insulating material inthe step-up coil layer; a still further layer of pressure tape disposedconcentrically over the further course of wire; a further layer ofinsulating material disposed circumferential over the further layer ofpressure tape; and a still further layer of pressure tape disposedconcentrically over the layer of insulating material.
 19. The coilarrangement of claim 17, wherein the further course of wire is wound byfewer turns than the course of wire.